In various industries (for example, the automotive, wind energy and aerospace industries), it is common practice to produce large, dimensionally accurate master models and tools. Models are used by engineers for the conceptual design of individual component parts of the final product. Tools are used for the creation of final parts. A model or prototype is usually used once or twice and is designated mainly on getting the external shape of an object. A tool or mould is designated to provide a negative of the external shape of the object and to allow manufacturing of the object itself, preferably several times. It follows that requirements for tools are more stringent than for making models.
U.S. Pat. No. 5,942,182 describes a resin transfer moulding (RTM) process used e.g. in the aerospace industry—comprises impregnating a fibre preform in a mould with a one component, room temperature stable, epoxy resin composition comprising a novolak resin, an epoxy diluent and a latent curing agent, typically a boron trichloride amine complex, to cure above specified temperatures.
The patent application WO 02/20261 describes making a seamless model comprising applying a mechanically frothed syntactic foam as modeling paste on the outer surface of a substructure, curing the paste and machining it.
A traditional method of making a tool, illustrated as “Traditional Process” in FIG. 1, involves making a mold from boards or SMP (Seamless Modelling Paste), applying a laminate on the backing structure, the laminate being further separated from the mold to produce a laminated tool. This method involves several different steps, it is lengthy and requires preliminary master model fabrication.
Another known method to produce large tools involves a “building block” approach in which several boards are glued together to produce a rough structure, which is then machined to form the desired shape. This approach, however, is both labour and time intensive and requires precision operations, leading to high cost, and moreover results in a model, which has visually perceivable bond-lines at the surface, an appearance which is aesthetically undesirable and may even cause surface defects on final parts.
U.S. Pat. Nos. 5,707,477 and 5,773,047 describe a method for making a model or tool including steps of:                fabricating a base with a top plate of aluminum,        bonding successive layers of perforated aluminum honeycomb core with a suitable adhesive until the desired height is reached,                    machining the stack of aluminum honeycomb core layers to the desired tolerance under the desired final contour,            applying a layer of syntactic epoxy to the machined aluminum core surface—this is accomplished by applying syntactic epoxy patties to the machined surface, and then forming the patties into a continuous layer by kneading the patties together and “seating” them into the core cells with moderate hand pressure,            curing the epoxy layer, machining it to the final contour desired, then seal the structure with an epoxy sealer                        
This method is illustrated as “Boeing process” on FIG. 1. However, this approach is again labour and time intensive, in that it involves stacking and bonding of the honeycomb core and hand application of the pliable solid patties. The method requires heating of the entire structure in order to cure the applied patties. The resulting models are also of relatively high density. Several different materials must be used, e.g. foaming adhesives and hand spread patties. The use of several materials can cause problems in matching the adhesive bond lines to the ultimate molding material.
U.S. Pat. No. 5,859,096 provides patties made of a one-component epoxy resin tooling material providing cured composition having high Tg and low Coefficient of Thermal Expansion CTE. The composition contains an epoxy resin, an epoxy diluent, a boron trichloride amine complex and a silica or silicate filler. The patties are butted together and rolled out to form a layer covering the substructure which is then heat cured.
Thus, there still remains a need for a model or tool and a method of producing models or tools, where the model or tool is characterised by low production costs, fast processes and a more uniform surface having improved smoothness and free of bondlines. Easy cutting, combined with machine (lathe, CNC or other forms) cuttability are desired attributes. Furthermore, there is growing need to produce tools which can withstand high temperatures, preferably greater than 120 C, more preferred greater than 150 C. Such temperature resistant tools in turn allow production of high temperature cure-able and resistant composites or laminates. In turn these composites are finding greater use as light weight strong objects in aerospace, auto, marine, wind energy, civil construction [eg leisure facilities, exhibitions, films and theater models). Such large models would benefit of having fire retardant properties.